1. Field of the Invention
The present invention relates to an IC memory card which has a credit card size, and a thickness of 2 to 4 mm, and in which a semiconductor memory, a control circuit for reading/writing the memory, and the like are mounted.
2. Description of the Related Art
Recently, two kinds of card-size storage media, i.e., IC cards and IC memory cards are popular.
Of these media, the IC cards have a thickness of 0.76 mm, and were developed to replace existing credit cards (magnetic stripe cards). The IC cards are also called "smart cards" since they can provide various functions. The IC card incorporates a one-chip CPU, and a semiconductor memory having a relatively small capacity (8 through 64 KB).
In contrast to this, the IC memory cards satisfy the international standard regulated by the ISO. The IC memory cards have dimensions corresponding to a credit card (85.6.times.54.0 mm), and a thickness of about 2 to 4 mm. The IC memory card incorporates a semiconductor memory having a relatively large capacity (16 KB to several MB), and a relatively simple control circuit for reading/writing the memory. IC memory cards of this type have the following advantages, and have received a lot of attention as future storage media. Thus, a wide application field of the IC memory cards is expected.
______________________________________ 1) compact, lightweight compact device 2) low power consumption long-time battery drive 3) high-speed access direct execution of program 4) high reliability very low error frequency 5) environmental wide temperature and resistance humidity ranges 6) portability easy carrying, and easy insertion/removal 7) wide application range various types (ROM, RAM, and the like) are available ______________________________________
FIG. 3 shows an outer appearance of the IC memory card.
In order to access the IC memory card, the following two access methods can be adopted. An external interface having the first or second access method is prepared for each card. The first method is a direct access method. In this method, a memory address is directly supplied from the external interface to access a memory. This method is used when a CPU of, e.g., a personal computer accesses a main memory, and allows high-speed memory access. The second method is an indirect access method. In this method, a memory address to be accessed is temporarily set in an address register in an IC memory card, and then, a memory is indirectly accessed. In the direct access method, although a time required for access can be shortened, the number of address signal lines is increased, and a memory address space of a CPU in a host apparatus such as a personal computer must be assured for an IC memory card.
In the indirect access method, since the number of address lines is small, an interface circuit scale in the host apparatus can also be small. Although the indirect access method does not require a memory access space in a CPU of a host apparatus, an address register must be arranged in the IC memory card, and a time required for access is prolonged more or less due to indirect access.
In this manner, the direct access method and the indirect access method have different features, and are used by utilizing their features. As a typical application, the direct access method is used when a program is directly executed on the IC memory card, since it allows high-speed access of the IC memory card. The indirect access method is used when a program or data is temporarily loaded from the IC memory card to a main memory of the host apparatus like a floppy disk, since the interface of the host apparatus is simple.
As described above, the direct access method and the indirect access method have different functions, and realize IC memory cards using unique interfaces. In general, the number of signal lines (terminals) in the direct access method is 34 to 68, and that in the indirect access method is 20 to 40.
Therefore, an IC memory card of the direct access method has no compatibility with an IC memory card of the indirect access method.
The IC memory cards have been expected as future information recording media, and various applications have been proposed. In order to use the IC memory card as a medium having a compatibility like a floppy disk, it is preferable that a single IC memory card can provide various functions while maintaining compatibility.